The present invention relates to control of antenna tilt and heading, and more particularly to an efficient system for adjusting antenna tilt and heading from the base of the antenna tower or from a remote site.
Cell phone systems are rapidly becoming a common mode of communications. The cost of using such systems has dropped rapidly over the past few years, and due to the convenience, many individuals rely solely on cell phones. The resulting substantial increase in use and the competition between service providers has provided significant motivation to maximize the efficiency of cell phone systems.
Cell phone systems involve the cooperation of cell phones operated by individual subscribers within the cells. The cells communicate with the cell phones and relay signals to central facilities which form connections with the desired destination which could be another cell phone or a conventional phone. An important characteristic of cell phone systems is controlling the interaction between cells and cell phones. Each cell generally covers an area on the order of about ten square miles. Signals transmitted between cell phones and cells are limited to low power levels so that the same frequencies may be used in non-adjacent cells. The ability to re-use the same frequencies is a very important characteristic of cell phone systems because the re-use of frequencies allows a much larger number of calls to simultaneously occur within a cell phone system.
A cell generally includes a cell tower (or base station) which includes antennas for transmitting and receiving signals from cell phones. A typical antenna configuration has three sectors aligned 120 degrees apart, thus forming a triangle. Each sector typically has three or four antennas. A single antenna, or a group of antennas defines a beam. The beam has a Maximum Response Axis (MRA) which is generally normal to the face of the antenna, but beams may be steered electronically to point the MRA away from being normal to the face of the antenna. The area covered by a given cell may be adjusted by either pointing (or steering) the beams, or by controlling power levels.
Cell tower antennas are initially adjusted to provide a desired cell coverage. However, over time both the physical orientation of the tower may shift, or the requirements for cell coverage may change due to new cells coming online, or due to usage changes. Further, changes in weather or construction of new structures may affect cell coverage. Traditionally, the most common antenna adjustment is adjusting down-tilt. Originally, adjusting down-tilt required a technician to climb the tower and manually adjust antenna mounting hardware to mechanically change the antenna tilt. Such manual adjustment was time consuming, costly, possibly dangerous, and required system downtime.
U.S. Pat. No. 6,239,744 for “Remote Tilt Antenna System,” describes a cell phone antenna system having an electronic tilt, and with antenna controllers associated with each antenna. Although the problems associated with manual tilt adjustment are addressed by the antenna system described in the '744 patent, the use of electronic tilt adjustment alters the shape of the beams. Because the antennas are designed to optimize beam shape for a non-steered beam, it may be assumed that electronic beam steering results in a less than optimal beam shape. For example, the main lobe of the beam may broaden, and/or side lobes may increase in width and/or amplitude. Further, the requirement for individual controllers for each antenna results in substantial cost and complexity, and the '744 patent does not address beam heading (i.e., azimuth).